Solution

ID: past-exam-of-the-mathematical-methods-ii-course-of-the-university-of-oxford/2016-resit/12/a/solution

For with continuous second partial derivatives near , its multivariable Taylor expansion is
where all displayed derivatives are evaluated at . Continuity of the second derivatives justifies equality of the mixed partials and the stated remainder. A cubic-order remainder requires additional regularity.

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